Serotype 5 and 8 capsule polysaccharide (CP5 and CP8) expression in Staphylococcus aureus isolates from patients with chronic bone infection.

LATTAR, SM; TUCHSCHERR, LPN; CACCURI, R; BARBAGELATA, MS; ALVAREZ, LP; BUZZOLA FR; SORDELLI, DO

Maastricht, Holanda

Simposio; 12th International Symposium on Staphylococci & Staphylococcal Infections.; 2006

Most clinically relevant S. aureus from human hosts produce CP5 or 8 CP8.  CP production may not be identical among different types of staphylococcal infections. This study was designed to evaluate the expression of CP5 and CP8 in isolates (n=117, from 99 patients) from a group of patients with chronic bone infection and to compare it with that of isolates (n=50) obtained from blood cultures of patients from the same setting with diverse diseases.  Species was confirmed by amplification of S. aureus specific ADN sequences. Clonality evaluation was performed by STAR-PCR.  CP5 and CP8 production was assessed by colony inmunoblot (screening) and immunodiffusion (final testing).   Production of alpha- and beta-haemolysin was performed by culture in rabbit and goat blood agar, respectively.  Biofilm production was assessed by culture on Congo red agar. A total of 61 bone infection isolates (52%) expressed CP5, 20 (17%) expressed CP8 and 36 (31%) were non-typeable (NT, non-CP5 and non-CP8). Further study of the NT S. aureus revealed that 50% exhibited positive amplification for cap5H-K specific genes, 40% for cap8H-K specific genes and that 10% did not show amplification for either cap5H-K or cap8H-K genes. Analysis of blood culture S. aureus isolates from the same nosocomial settings as those described above revealed that 33 of them (66%) were CP5, 17 (34%) were CP8 and none were NT. Several clones, with prevalence of two of them associated with MRSA were detected among the isolates.  No differences were found in alpha-, beta-haemolisis or biofilm production among the groups under scrutiny.  Evaluation of multiple samples from the same patients over time showed the presence of isolates with similar genealogy with and without CP production. Our results suggest that NT S. aureus may be selected during chronic bone infection.  The selecting factor that exerts pressure on CP5 and CP8 S. aureus rendering some of them NT remains undisclosed and merits further research.